1. Field of the Invention
The invention relates to a tubular joint, in particular of the type used for hydrocarbon wells or the similar wells, e.g. in the field of geothermics.
2. Description of the Related Art
Such a joint may exist between two large-length tubes or between a large-length tube and a coupling. These joints are used in particular for assembling strings of casings or tubings. Taking into account the mechanical features required, the casings and tubings are generally composed of heat-treated steel.
For their part, the joints must withstand tension, compression, bending and sometimes twisting as well as widely differing pressure in both directions between the inside and the outside. Furthermore, they must even be gas-tight, at least in certain cases. Threaded joints are particularly advantageous in this respect.
However, it is currently intended to subject the tubes in situ to diametric expansion with permanent plastic deformation. This has various advantages, which will be referred to below. Again it is necessary that the joints remain operational after the plastic deformation due to diametric expansion to which they are subjected like the tubes. Thus it is desirable that the threaded joints hold after plastic diametric expansion whilst substantially retaining the features for which they are valued, in particular mechanical strength under tension/compression, with or without internal or external high pressure, as well as sealing-tightness.
As will be seen below in detail, the conventional joints are not entirely satisfactory: either they do not meet these requirements, or they meet them in a random manner, or they meet them, but not in a repeated manner.
In the not yet published international application PCT/FR01/02005 by the Applicants, a joint structure is proposed which is intended to withstand plastic diametric expansion.
The sealing-tightness of the tubular joints depends on the effective contact area of the sealing faces, which is affected by the presence of irregularities resulting from the machining of these surfaces. Furthermore, these irregularities are apt to be pulled off when the sealing faces of the two tubular elements slide over one another during assembly of the joint, and likewise during radial expansion where this is provided, thus causing further deterioration of the quality of their contact.